Apparatus for reducing particle size



May 6, 1969 E. H. CUMPSTON, JR 3,442,457;

APPARATUS FOR REDUCING PARTICLE SIZE Sheet Filed July 50, 1965 50%4160 m COM/U70, 72

ATTORNEY May 6, 1969 E. H. CUMPSTON, JR

APPARATUS FOR REDUCING PARTICLE SIZE Sheet Filed July 50, 1965 INVENTOR fax/4,20 H. CUMPfm ZR BY 4 v w ATTORNEY! May 6, 1969 E. H. CUMPSTON, JR 3,442,457

APPARATUS FOR REDUCING PARTICLE SIZE 3 f 0 3 4 A t m e E m T S 4 W m in 0 2 F[ mm fr 7 A M Z III W R 5 0 1 WM M 4 M Q 1 3 AF AW J4 m WW J J m d A .m T 1 F NEUTRAL Int. Cl. B02c 4/00 U.S. Cl. 24147 49 Claims ABSTRACT OF THE DISCLOSURE A device for reducing the particle size of cellulose fibers includes a rotor and stator with irregular confronting surfaces forming a narrow particle reducing passageway. Gas is formed through the passageway to carry particles from the input to the output end of the passageway, and at least a portion of the passageway is arranged to proceed radially inward so as to be uphill relative to centrifugal force. This causes larger particles of greater mass to be retarded or thrown back in the passageway by centrifugal force until they are sufliciently reduced to be carried through the passageway by the opposing gas stream. The reducing surfaces are preferably formed by ridges and grooves, and the rotor and stator are preferably built up in laminated form. The reducing passageway preferably extends along a radial face of the rotor at its input end, across the circumferential surface of the rotor, and radially inward along a radial face of the rotor at the output end of the passageway.

This invention relates to a device for reduction of particle size and is particularly adapted for use in reducing wood chips to pulp of the type commonly known as ground wood, the major constituent of newsprint paper. In particular, this invention relates to a device that reduces the particle size in stages and with a degree of uniformity not found in existing devices.

In the past, ground wood has been produced by pressing a log against a grinding stone. The grinding process gives a wide range of particle sizes, from unwanted fines through good fibers and up to unusable splinters which must be removed. In recent years, much work has been done on replacing the grinding process with high speed, counter-rotating discs between which wood chips are fed. The resulting pulp usually produces stronger paper because of a higher percentage of good, long fibers. The power requirements of discs, however, are excessively large, and control of the machines is extremely sensitive. This machine control involves disc grooving patterns, disc wear, and constant material feed rates. Even more important, perhaps, the control involves extremely close regulation of the clearance between the rotating discs. Disc clearances run on the order of 0.005 inch. An increase of 0.001 inch or so reduces particle retention time and results in an excessive number of splinters in the finished product; a reduction of 0.001 inch or so, increases retention time and produces fines and sometimes even burning. In addition, these disc machines are necessarily very large, high speed (up to 12,000 surface feet per minute), and high powered (800 horsepower). High power results in large temperature variations which distort the machine, emphasizing the difliculties of controlling the clearance. The basic nature of the machine thus makes United States Patent can result in wide variations in product quality.

My invention obviates these problems by the use of a sequential grinding system using stages or zones. In the first zone, air flow and centrifugal force work together to drive the material. In subsequent zones, air pressure opposes forces due to centrifugal force. The result is that these respective forces, working in opposition to one another, serve to differentiate the particle size and produce the desired uniformity.

The apparatus of my invention also utilizes a simple adjustment means whereby the device may be varied to handle different materials and produce dilferent degrees of fineness in the finished product. This is effected by use of a laminated structure in either the rotor or stator, or both, which permits adjustment of surface characteristics.

Accordingly, the advantages of my invention include:

(1) The use of multi-stage sequential particle reduction to give the best control of product particle size.

(2) Continuous classification of particle size in each stage of the processing providing for removal of particles of the desired size from that stage before they are overworked, but continuous retention and working of other particles not reduced sufiiciently.

(3) Ready control of process by varying the velocity of the driving stream of air, the angle of certain groove structures in the zones, and the grinding clearances.

(4) The compactness and simplicity resulting from using all three surfaces of a single rotating disc to produce a three-stage operation with efficient use of maximum surface speeds. Greater grinding clearances allow simpler bearings and greater surface speeds.

(5 Single pass operation, eliminating screening and reworking of the product.

(6) Longer wearing grinding surfaces resulting from larger clearances, the use of deeper, more open grinding grooves, coiled tooth strips, and better classification of particle size in each stage.

(7) Increased power efiiciency, since finished size particles are not reworked and the likelihood of occurrence of over-sized particles in the wrong stage is greatly reduced.

(8) Simplicity and economy of design, making for eflicient operation.

Turning to the drawings:

FIG. 1 is a sectional view taken axially of the apparatus of my invention, showing the construction thereof;

FIG. 2 is a section taken along lines 2-2 of FIG. 1, showing the angularity and adjustability of the angularity 0f the stationary grooves in the second stage of my invention;

FIG. 3 is a simple schematic drawing showing the operation of the device;

FIG. 3A is a modification of a portion of FIG. 3, showing a simple method of varying grinding clearances;

FIG. 4 is a partial section taken on line 4-4 of FIG. 3 to shown certain operating details;

FIG. 5 is a section taken on line 5-5 of FIG. 4;

FIG. 6 is an elevation of a portion of the inside surface of the stator showing types of adjustments of the stator surface possible with the laminar construction of the stator of my invention;

FIG. 7 is a transverse section of the rotor of my invention, showing a modification thereof; and

FIG. 8 is an end elevation of another form of rotor of my invention.

FIG. 1 depicts in section the grinding portion of my invention. It includes grinding disc or rotor I mounted upon axle 2 and supported by bearings 3. Grinding rotor 1 is circular in cross-section and is rotated by rotation of the axle 2 by a customary power source, not shown.

Rotor 1 has forward surface 5, peripheral surface 6, and rearward surface 7, which, as will be described later, define respectively, the first, second and third stages or zones of grinding.

Surrounding rotor 1 is a casing or stator 10 having, as parts thereof, inlet disc 11, breaker laminations 12 and outlet disc 13. Disc 11 is spaced from forward surface and thereby defines a first grinding zone. Laminations 12 are spaced from the peripheral surface to define a second grinding zone, and outlet disc 13 is spaced from rear surface 7 to define a third grinding zone. The three zones formed by rotor 1 and stator define an integral passageway for the material to be ground. The respective rotor and stator surfaces are substantially parallel in the first and third zones, and may be parallel or converging in the second zone.

The entire unit is mounted in a frame depicted generally by the numeral 20. Secured to frame 20, along the axis of rotor 1, and adjacent to forward surface 5 is air inlet 22. Positioned adjacent to this on frame 20 is chip inlet 23, having, as a portion thereof, the hopper or entry for chips 24 and provision, if desired, for a feeding mechanism, such as a screw or plunger, at 25. Since the air inlet of the unit is nearer the axis than is the outlet, a differential pressure is created which normally makes the unit self-feeding and self-circulating.

Surface 5 has formed thereon a series of radial grooves 30. Similarly, inlet disc 11 has radial grooves 32. These may be spaced as desired, but preferably the clearance is great enough to keep the production of fines at an absolute minimum, since in this first stage it is desirable to cause only an initial coarse breakdown of the wood chips, through shearing action.

Peripheral surface 6 is frusto-conical for clearance adjustment with its wider diameter adjacent the inlet end 23. It has on its surface a series of grooves running generally in the axial direction. Opposing it are laminated discs 12, described below, but which in general are made up of a series of circular discs, one of which, for example, would be disc 35. These discs each have a plurality of holes, such as 36 and 37, in their periphery and are held together by bolts, such as 38 and 39, passing through the holes and connected to casing 20.

The innermost edges 40 of discs 12 are preferably of scalloped configuration. When the discs are mounted in frame 20 the scalloped configurations are generally aligned to define a series of grooves 41 running either in an axial direction or at an angle to the axis. The inner diameter of these laminated discs 12 varies uniformly from disc to disc, with the smallest diameter being farthest removed from the input end and the greatest diameter being near the input end, but preferably opposite the widest portion of rotor 1, that is, adjacent the input end of surface 6. Centrifugal force thus slightly opposes throughput.

Edges 40 may be cut sharply transverse to the planes of the respective disc 12 or they may be cut at a slight angle corresponding to the angularity of the groove formed when the discs are assembled.

Preferably, the number of scallops in the circumference of the discs differs from the number of holes. For example, each disc might have 16 holes and scallops. Thus, when bolts 38 and 39 are removed, the discs 12 may be rotated about the axis of rotor 1 and the individual laminations may be rotated relative to one another to change the groove angle. Bolts 38 and 39 are then replaced and tightened before the unit is operated so that the laminations 12 are secured against movement relative to frame and relative to one another.

Outlet surface 7 has defined therein a series of radial grooves 50. These grooves preferably extend from surface 6 for a distance of about a quarter of the way from surface 6 to the axis of rotor 1. The grooves have an innermost end 51. Facing surface 7 is outer disc 13, also having stationary radial grooves therein 53. Grooves 53 extend from the periphery of outer disc 13 to a point, defined by end ring 55, which is farther removed from the axis than is end 51 of grooves 50.

Ring 55 and end 51 define an exit 54. As can be seen, exit 54 is farther removed from the axis than is air inlet 22, resulting in a pressure differential causing air to flow through the unit. Adjacent exit 54 is outlet 60, leading to outlet tube 61.

Associated with axle 2 is a motor or other driving means (FIG. 3) adapted to rotate rotor 1. Similarly, adjacent air inlet 22 are means, if desired, not shown, for compressing air and driving it inwardly through tube 22 in the direction shown by the arrow. Valves may be included therein as is necessary. Exit 54 can be kept large so air flow is self-sustaining.

FIG. 2 shows a partial section on line 22 of FIG. 1 of laminated discs 12 having edges thereon 40 defining grooves 41. In operation the rotor rotates in the direction shown by the arrow in FIG. 2. Thus, as can be seen, the scalloped portions of the inner edges 40 of laminations 12 define grooves preferably of an asymmetrical shape. The leading edges of the grooves 65 approach tangency with the direction of rotation, lead down to the troughs 66, and then to the sharper driving surface 67, the angle of which approaches an angle of about 35 with the radial. Shifting of the laminations 12 relative to one another and with a greater degree of shift in the outlet portions than in the inlet portions will cause the grooves to form a spiral passageway.

The spiral nature of this passageway is shown in FIG. 6. This is a view from adjacent the axis looking toward a portion of laminations 12. The material being processed moves from left to right in the drawing, and peripheral surface 6 of the rotor moves downwardly relative to the surface of stator 10 defined by laminations 12. By presetting the angular positions of laminations 12 relative to one another, the edges 40 causes grooves to be formed which are neutral to material flow, assist in the feed of material, or oppose the feed and so tend to hold the material, as shown in the respective three sketches of FIG. 6.

In FIG. 3 the unit and its operation are depicted more schematically. Shown generally are rotor 1, laminated surface 12, an air inlet 22, the inlet 23 for wood chips or the like, and the outlet 61. Also shown is a motor 70 for actuation of axle 2 and rotor 1. The arrows in FIG. 3 show the direction of air and material flow through the unit. Shown by brackets is the first grinding stage A defined by surfaces 5 and 32; the second grinding stage B defined by surfaces 6 and grooves 41, and the third grinding stage C defined by surfaces 7 and 13.

FIG. 3A shows a modification possible which enables more ready adjustment of the spacing between .rotor surface 6 and stator surface 40. Blocks 14 and 15 hold laminations 12 and permit adjustment in an axial direction relative to inlet disc 11 and outlet disc 13. As can be seen, such axial adjustment will result in greater or less spacing between surfaces 6 and 40.

FIG. 4 is a section somewhat schematic on line 44 of FIG. 3 showing grooves 41 of laminations 12 in their positions opposed to grooves 9 of surface 6. The spiral direction that grooves 41 follow is shown. The arrow on surface 6 shows the direction of motion of the surface relative to the laminations.

FIG. 5 depicts the inner peripheral surface of stator 10 with laminations 12 having grooves 41 therein opposed to surface 6 of rotor 1. This figure also shows the generally axially aligned grooves 9 to surface 6. The conical configuration of surface 6 with the wide radius toward the entrance is also depicted here, as is the inner conical configuration produced by laminations 12.

As previously mentioned, the apparatus of my invention is built around a single high speed rotating disc or grinding rotor 1 positioned within stator 10. The refining of particles size is done in three separate and distinct stages or zones, A, B and C, shown in particular in FIG. 3. A large volume of air or, if desired, steam or other gas is admitted at entrance port 22 and sweeps through the three refining zones and out at the circular discharge 60 and outlet 61. The rotation of disc or rotor 1 serves to circulate the air through the machine, but if desired a blower (not shown) may be used to increase the fiow. A valve may be used at entrance port 22 to regulate the air fiow.

Material to be refined enters at port 23 adjacent the rotor axis. The inlet port may, if desired, be bafiled to prevent air flow.

In the first stage area or zone A, the initial coarse breakdown occurs. The open grooving 32 and 30 on surfaces 11 and 5 respectively serve to accomplish this purpose. In zone A, both centrifugal force and air motion speed material through the zone, keeping retention time in the zone short, thus producing a fast, eflicient, initial size reduction.

Second stage grinding area or zone B accomplishes the major portion of its work at the periphery of the rotating disc or rotor 1 where the surface speed is the highest. The material feeds from zone A into zone B and as it enters is of more or less uniform size as a result of the action in zone A. Retention in zone B is controlled by the air sweep and the grooving arrangement. Because of the conical shape of this zone, centrifugal force has a tendency to retard particle throughput, since the greater radius along the surface is toward the input end. In addition, as has been mentioned, the stationary grooving 12 can be given a screw thread lead or grooved spiral; it can be so set as to tend to throw particles back toward zone A to any extent desired. The larger particles are spun harder into the stationary grooving by rotating disc 1, so their retention is more pronounced. As particle size is reduced, the centrifugal force on them is also reduced.

Thus, in zone B, we find that the air sweep tends to carry the particles from zone B into zone C, but centrifugal force tends to hold the particles back. According to Stokes Law, the air pressure upon the particles relative to the centrifugal force will be greater on the smaller particles. Thus, the smaller particles tend to pass through while the larger particles are retained in zone B. The retention of larger particles continues until their size has been reduced to that desired.

The refining action in zone B results largely from impact, and so does not tend to produce harmful fines. The larger and harder wood splinters are carefully knocked apart by repeated high speed impact, while the softer splinters are quickly reduced and blown along toward zone C.

As can be seen from FIG. 4, the grooves 9 in surface 6 are more open than would usually be found in grinding devices so material does not lodge in the grooves. To insure free material movement and continuous impacting, the stationary grooves 41 formed by laminated discs 12 are also open, with their leading edges tangential to the disc rotation, curling back to throw material into the disc again. The stationary grooves are rotationally staggered to give any desired reverse-feeding spiral to the particles. The rotational air motion imparted by grooves 9 of surface 6 keep the material particles in constant suspension so that the air sweep is always tending to carry them on to zone C. The clearance between the rotating grooves 9 and the stationary grooves 41 may be adjusted in any desired manner simply by moving laminations 12 in an axial direction. Normally the clearance is several times that necessary for mechanical shearing to the desired particle size.

The shape of grooves 41 is important. If the re-entrant curve is too sharp, material lodgments may occur. This will then allow the machine to do mechanical shearing action and also will negate the classification of particle size through the inner sweep versus centrifugal force motions. If the re-entrant curve is too gentle, the impact forces will be reduced and efficiency lwill sufler. A reentrant angle of about 20 to 60 degrees, and preferably about 35 degrees to the radial appears to be a good compromise.

Particles small enough to be swept into zones C are very close to being satisfactory for a finished product for most purposes; they are light and less susceptible to impact grinding. The operation of zone C is primarily one of mechanical shearing. =It may, however, be of a type not found in normal refining apparatus, because the particles have been previously classified to a substantially uniform size; thus, mechanical shearing can be accomplished without serious fiber damage. Also, it will be noted that the flow of material is opposite from that normally found, i.e., it flows from the greater diameter section of rotor 1 to the smaller diameter section. This axial flow of material again causes self-classification of particle size, for centrifugal force will keep the larger particles in the system and enable them to oppose the inwardly moving air flow. The smaller particles, however, may pass out- Wardly between the end 51 of grooves 7 and ring 55 into outlet 60 adjacent the axis of the rotor. Once past ring 55, the air sweep carries the final product out the discharge 61 without further refining.

Though this apparatus is primarily designed to manufacture mechanical pulp, the features disclosed should be applicable to many other grinding operations.

If desired, in the operation of this machine, heat and/or chemicals may be added to the grinding process. As can be seen, the more difiicult a particular particle is to grind, the longer it will be retained against the sweep of air and so will receive more heat or'chemical treatment.

The air or stream used to cause flow through the unit can, if desired, be picked up from a separating cyclone and recirculated through the unit.

Instead of, or in addition to, having a laminated stator, the rotor 1 may also be of laminar construction, allowing grooves 9 to have an adjustable spiral configuration. This modification is shown in FIG. 7.

In FIG. 7, rotor 1 includes a plurality of laminated discs 75 bounded at the ends by grooved forward surface block 5 and rearward surface block 7. These discs 75 have a saw-tooth periphery 76, defining grooves. Teeth 76 may be in alignment or out of alignment, providing for a spiral groove, which is shown by dotted line 80. The shape and degree of angularity of-the grooves defined by discs 75 of rotor 1 may be varied as desired, just as with discs 12 of stator 10. Preferably, these angles may be set by having a different number of positioning holes 77, held by bolts 78, from teeth 76.

FIG. 8 shows a modification applicable to inlet disc 11 and outlet disc 13. Here the teeth, such as 80, are on the edge of a preshaped and tooth-hardened metallic strip 81. This strip is then spirally wound and placed on the surface of the disc, and is adhesively secured thereto with, for example, an epoxy resin. The winding may continue, if desired, to almost the center. Teeth 80, together, preferably define a series of grooves, which may be of random or pre-determined pattern, upon the surface of disc 11 or 13.

Use of the coiled strip 81 serves to increase the working edge by a factor of about 2 /2 to 10 and allows for any degree of hardening desired without fear of cracking the disc.

It will be clear to those skilled in the art that many variations of the invention herein disclosed can be made without departing from the spirit thereof. For example, rotor 1 on shaft 2 with its associated bearings and drive may all be axially adjustable so that the clearance between rotor 1 and outlet disc 13 can be varied. It will also be evident that the transition between zones should normally be kept smooth and consistant to prevent material from lodging therein.

Iclaim:

1. An apparatus for sequential grinding of material including a rotor and a stator, said rotor and stator defining an integral passageway for material to be ground, said passageway having a first, a second, and a third grinding zone, means for forcing material sequentially through said zones under gaseous pressure, said stator and rotor surfaces each having confronting grooves in said first zone, confronting grooves in said second zone, and confronting grooves in said third zone whereby said material is ground therebetween and whereby the size of said ground material and the period of retention of said material in said apparatus is controlled by gaseous and centrifugal forces on the particles of said material.

2. The apparatus of claim 1, in which the said surfaces in said second zone are parallel and at an angle to the axis of said rotor.

3. The apparatus of claim 1, in which said stator grooves in said second zone are spiral.

4. A particle grinding machine comprising a rotary element having a periphery structured for grinding, means for supporting and rotating said element, a stationary disc adjacent and spaced from each side of said rotary element, the surfaces of said stationary discs confronting said rotary element being structured for grinding, a stationary hollow member enclosing said rotary element and the adjacent space between said stationary discs and having a grooved interior surface adjacently surrounding the circumference of said rotary element for co-action therewith, one of said stationary discs including an opening therein for supplying material to be ground between said stationary element spaced radially inward from the circumference of said rotary element and said rotary disc, and the other of said stationary discs including an opening therein for the discharge of the ground material.

5. A particle grinding machine as specified in claim 4, in which the circumference of said rotary element and the interior surface of said hollow member have the shapes of cones with their larger diameters adjacent said one stationary disc provided with said material supply opening.

6. A particle grinding machine as specified in claim including means for moving said hollow member in an axial direction to vary the clearance between the circumference of said rotary element and the interior surface of said member.

7. A particle grinding machine as specified in claim 4, in which said stationary hollow member is formed of a plurality of grooved laminations mounted with the grooves of adjacent laminations in conducting relation with one another to thereby form continuous grooves extending across said interior surface of said member.

8. A particle grinding machine as specified in claim 4, in which the grooves of said interior surface of said stationary member have their material receiving ends extending substantially tangentially to the circumference of said rotary element and are then smoothly curved in the direction of rotation of said element and back into proximity with the circumference of said rotary element.

9. A particle grinding machine as specified in claim 4, in which the grooves of said interior surface of said stationary member are curved in the direction of rotation of said rotary member and inclined spirally in a direction transverse to said interior surface of said stationary member.

10. An apparatus for particle grinding including a rotor and a stator mounted together for co-action, said rotor being mounted for rotation about its axis, means associated with said rotor to rotate it at high speed, said rotor including an inlet surface, a circumferential surface, and an outlet surface, said inlet surface and said outlet surface having substantially radial grooves therein, said circumferential surface having substantially axial grooves therein, said stator including inlet, circumferential, and outlet surfaces spaced from and facing said respective inlet, circumferential and outlet surfaces of said rotor, said inlet, circumferential and outlet surfaces of said stator being grooved, an inlet adjacent the axis of said rotor for introducing material to be ground, means for introducing a gas between said inlet surfaces of said rotor and of said stator, and an outlet spaced radially inward from said circumferential surface of said rotor for receiving said ground material and said gas from between the said outlet surfaces of said rotor and said stator.

11. The apparatus of claim 10, in which the grooves on said circumferential surface of said rotor are parallel to the axis of said rotor and are displaced from said circumferential surface of said stator sufiiciently to prevent shearing action on the material being processed.

12. The apparatus of claim 10, in which said grooves on said circumferential surface of said stator are disposed at an angle relative to the axis of said rotor.

13. The apparatus of claim 10, in which said grooves on said circumferential surface of said stator are formed by a lamination of a plurality of layers of planar material having grooves in the circumference thereof, said layers being offset angularly relative to one another.

14. The apparatus of claim 10, in which said grooves on said circumferential surface of said stator are substantially tangential to said rotor along the leading edges of said grooves and are at an angle of about 35 degrees to the radial along the trailing edge of said grooves.

15. The apparatus of claim 10, in which said circumferential surfaces of said rotor and said stator are parallel and at an angle to the axis of said rotor.

16. The apparatus of claim 10, in which said grooves of said stator are formed by a lamination of a plurality of layers of planar material.

17. The apparatus of claim 10, in which the inner ends of said grooves in said outlet surface of said stator end a distance farther removed from the axis of said rotor than the inner ends of said grooves on the outlet surface of said rotor, and said outlet is farther removed from said axis than said inlet.

18. A particle grinding machine including a grooved disc mounted for rotation, means for rotating said disc at high speeds, two stationary discs mounted adjacent but spaced from opposite sides of said rotating disc for grinding co-action therewith, said stationary discs having substantially radial grooves therein, the circumferential surface of said rotating disc having a frusto-conical configuration and generally axial grooves therein, a frame having a stationary internally-grooved surface positioned surrounding said conical surface to co-act with said circumferential surface of said rotating disc, a material inlet positioned adjacent the axis of one of said stationary discs, a gas inlet associated therewith, a material outlet positioned adjacent the axis of said rotating disc and on the opposite side thereof from said gas inlet, said stationary discs and said stationary surface being integral whereby, in conjunction with said rotating disc, they provide a unitary passageway from said inlet to said outlet for material being processed.

19. The apparatus of claim 18, in which the said internal grooves of said internally grooved surface have their leading edges substantially tangential to said circumferential surface of said rotating disc and said grooves have a smoothly curved re-entrance to the proximity of the rotating disc.

20. The apparatus of claim 18, in which said internal grooves of said stationary surface have a re-entrant angle of between about 20 and about 60 degrees to the circumference of said rotating disc.

21. The apparatus of claim 18, in which said internally grooved surface is formed of a series of layers of laminated material transverse to the axis of said rotating disc and said layers are mounted to allow angular shifting relative to one another to vary the angle of said internal grooves, and to expose more grinding edges.

22. The apparatus of claim 18, in which at least one of said stationary discs includes a flat face, a metallic strip having teeth on one edge thereof, said strip being wound in a helix with its teeth on one surface thereof, said teeth defining said radial grooves, and the other surface of said helix being secured to said face.

23. In an apparatus for particle grinding which includes a rotor and stator mounted together for coaction, the surfaces of said rotor and said stator defining a passageway from an inlet adjacent the axis of said rotor at one side thereof and an outlet adjacent said rotor at the other side thereof, a means for providing a variably grooved surface on said stator along the circumference of said rotor, said means including a plurality of grinding plates mounted together in laminar fashion with their planes substantially transverse to the axis of said rotor, said mounting permitting rotational movement of said plates relative to one another about the axis of said rotor, said plates having grooves therein along their edges most adjacent to said rotor, said grooves together defining a plurality of grooves along said surface.

24. The apparatus of claim 23, in which said grooves of said plates together define a plurality of grooves having a spiral configuration.

25. In a particle grinding machine having a stator with inlet, circumferential and outlet surfaces, and openings in said inlet and outlet surfaces, respectively, proximate to the axis of said stator to admit and discharge material being processed in said machine, a rotor having a frustoconical configuration, positioned within said stator, and mounted for rotation about an axis common with said stator, said rotor including a plurality of generally circular discs of sheet material secured together about said axis, said discs having a plurality of transverse grooves about the circumference thereof, and said grooves of said discs together defining a series of grooves upon the circumferential surface of said rotor.

26. The rotor of claim 25, in which the end surfaces thereof, transverse to the axis of said rotor, include radial grooves.

27. A rotor for use in association wtih a stator in a particle grinding machine, said rotor including a plurality of generally circular discs of sheet material, means for securing said discs together in plates transverse to the axis of said rotor so as to prevent rotational movement of said discs relative to one another, said discs having a plurality of transverse grooves about the circumferences thereof, and said grooves of said discs together defining a series of grooves upon the circumferential surface of said rotor.

28. The rotor of claim 27, including means for varying the angular position of said discs relative to one another to thereby vary the direction of said grooves.

29. An apparatus for particle grinding including a stator, said stator having at least one circular planar surface having grooves therein, said surface including a flat face, a metallic strip wound into a helix and secured to said face, and teeth on the edge of said strip removed from said face, said teeth together defining a series of grooves on said plannar surface.

30. The apparatus of claim 29, in which said grooves are -of generally radial configuration.

31. An apparatus for particle grinding including a stator, said stator having at least one planar surface, said planar surface having a flat face, at least one metallic strip secured to said face, said strip having grinding teeth thereon on the surface thereof most removed from said face, and said teeth together defining a series of grooves on said planar surface.

32. In particle reducing apparatus including a rotor and a stator having adjacent surfaces configured for reducing said particles upon rotation of said rotor relative to said stator, the improvement comprising:

10 (a) said surfaces being arranged to define a narrow, continuous passageway for said particles between said reducing surfaces of said rotor and said stator, said passageway having a plurality of working zones; (b) means for forcing gas through said passageway from the input end of said passageway toward the output end of said passageway to urge said particles through said passageway; and

(c) a preceding zone of said passageway being radially further from the axis of said rotor than a succeeding zone of said passageway so that centrifugal force from said rotation forcing said particles away from said rotor axis urges the larger of said particles toward said preceding zone in opposition to the force of said gas urging said particles toward said succeeding zone.

33. The apparatus of claim 32 wherein said preceding zone is arranged along the circumference of said rotor and said succeeding zone is arranged along a radial face of said rotor.

34. The apparatus of claim 32 wherein the circumferential surface of said rotor is generally frusto-conical and said preceding zone comprises a larger radial region of said frusto-conical surface and said succeeding zone comprises a smaller radial region of said frusto-conical surface.

35. The apparatus of claim 32 wherein said reducing surfaces are formed with lands and grooves.

36. The apparatus of claim 32 wherein said rotor is generally cylindrical and said working zones comprise a first zone arranged along a radial face of said rotor at the input end of said passageway, a second zone arranged along the circumferential surface of said rotor, and a third zone arranged along a radial face of said rotor at said output end of said passageway.

37. The apparatus of claim 36 wherein said reducing surfaces of said rotor and said stator in each of said zones are each formed with a respective set of ridges.

38. The apparatus of claim 37 wherein said ridges on said circumferential surface of said rotor and the corresponding adjacent surface of said stator are inclined relative to each other.

39. The apparatus of claim 36 wherein said stator is formed of a plurality of annular rings secured together to provide radially inward projecting ridges adjacent the circumferential surface of said rotor.

40. The apparatus of claim 32 wherein said stator in said third zone comprises a metallic strip wound into a planar helix, said strip having teeth along an edge thereof so that said teeth extend from a face of said helix to form a grinding surface.

41. The apparatus of claim 40 wherein said teeth are hardened and each convolution of said helix engages adjacent convolutions to form a tightly wound coil.

42. The apparatus of claim 36 wherein the circumferential surface of said rotor and adjacent surface of said stator are each formed with a respective set of ridges and grooves, and wherein the grooves in said stator have their material receiving ends extending substantially tangentially to said circumference of said rotor and have a smoothly curved re-entrance to the proximity of said rotor, said re-entrance forming a ridge.

43. The apparatus of claim 36 wherein said circumferential surface of said rotor is frusto-conical with its larger radius adjacent said radial face at said input end of said passageway.

44. A grinding element for use in a particle size reducing device, said grinding element comprising: a metallic strip wound into a planar helix, said strip having teeth along an edge thereof so that said teeth extend from a face of said helix to form a grinding surface.

45. The grinding element of claim 44 wherein each 47. The grinding element of claim 44 wherein said 5 teeth are evenly spaced along said strip.

48. The grinding element of claim 45 wherein the edge of said strip opposite said toothed edge is linear to form a smooth face of said helix opposite said grinding surface, and said smooth face of said helix is secured into 1 engagement with a backing plate.

49. The grinding element of claim 44 wherein said teeth are generally rectangular.

References Cited UNITED STATES PATENTS 2,153,537 4/ 1939 Heath et a1 241-220 2,464,733 3/1949 Traylor 241-105 2,893,649 7/ 1959 Mischanski 241-408 X 3,053,297 9/ 1962 Brundler 24-1-90 3,074,555 1/ 1963 Ruozinski 241-91 X 0 GERALD A. DOST, Primary Examiner.

US. Cl. X.R. 

